Ordinarily, gravity is used to pull logging tools along and into a well borehole for conducting logging operations. When a well is highly deviated, the gravity vector may not draw the logging tool through a deviated portion of the well. Many oil wells are deviated; this is particularly the case at an offshore platform where many wells are drilled from the platform into a targeted formation. While some of the wells might be approximately vertical, most of the wells extending from the platform will deviate at various angles into the formations of interest and some may involve deviations as high as about 75.degree.. Gravity conveyed logging tools supported on wirelines do not necessarily traverse the deviated hole to the zone to be logged. Rather, the logging tool must be pushed through the deviated well to the zone of interest to assure that the logging tool is located at the requisite location in the deviated hole. It is desirable therefore that the logging tool be fixed to the end of a string of drill pipe to assure measurements along the deviated well and orientation of the logging tool at the zone of interest.
In a deviated well, the logging tool must be initially positioned in the open borehole to assure that the logged data is properly referenced to the zone of interest. In a vertical borehole, the logging tool typically will be positioned axially of the borehole. In fact, successful logging can be obtained with tools which are centralized in the open borehole and also for those which are forced to the side of the borehole for decentralized operation. The present system is particularly able to support all types of tools in a logging tool assembly and position the decentralized tools so that they are located in a known position relative to the gravity vector.
Consider a deviated well where the well is more than 10,000 feet from well head drilling apparatus to the zone of interest. Assume further that the deviated portion of the well is at a high angle, perhaps as high as 75.degree. or 80.degree. with respect to vertical. The high side of the hole with respect to the gravity vector is the top of the borehole while the low side is the bottom of the deviated borehole. In this example, if one desires to position a logging tool in the deviated region, the logging tool is positioned so that the decentralized tool faces the low side of the deviated borehole. Should the tool be at some other angle, then rotation of up to 180.degree. must be imparted to the logging tool. This has been handled in the past by incorporating some kind of motor between the drill string and the logging tool. The motor is rotated to thereby rotate the logging tool until it is properly positioned relative to the gravity vector. If the motor is omitted, the entire drill string can be rotated from the well head. This is not particularly desirable because rotation from the well head may require substantial rotation on the drill string before the logging tool is rotated. The drill string comprised of steel pipe responds as a resilient member and may absorb some rotation and thus will not deliver the required rotation in a controllable fashion. In other words, carefully calculated rotation cannot always be imparted from the well head to the logging tool through the resilient drill string. Rather, the rotation of the tool will be irregular, subject to snagging, or the rotation may be absorbed entirely in the drill string. It is a matter of chance that the drill string can manipulate the logging tool to the proper decentralized orientation relative to the high side and low side of the deviated well.
The present invention sets forth a method and apparatus in which the logging tool can be positioned so that the high side of the hole is properly oriented to the high side of the logging tool. The present apparatus supports a logging tool so that it seeks the low side of the hole and stays oriented at all times in the deviated well. By contrast in the vertical wells, azimuthal orientation is not usually important. When the deviated portions are encountered, the present apparatus positions at all times the logging tool so that it is decentralized and positioned against the low side of the borehole. This is true without regard to the angle of deviation. That is, it can be used where the well is deviated perhaps only 30.degree. but is also can be used where the deviation approaches the horizontal.
The logging system of the present disclosure further includes a connector system which enables deferred connection of the logging cable to the logging tool. This is highly desirable so that movement of the drill string occurs without involving the logging cable. The drill string is assembled with a side entry sub located in the drill string. The side entry sub is positioned in the drill string at a specified depth, as will be explained, below the well head. The drill string is maneuvered until the logging tool is at the start of the zone of interest. Then, the mud flow through the drill string is used to force a wet connector with associated apparatus along the drill string to land in contact with the mating connector at the logging tool. This deferred connection of the electrical conductor with the logging tool permits all the maneuvers to be completed prior to the actual logging sequence. Thus, the logging tool is at the zone of interest, poised for logging sequences to be conducted in that zone, properly oriented with respect to the gravity vector, appropriately decentralized, and positioned against the low side of the deviated well. At this juncture, the next step is to begin adding drill pipe to the string at the surface to force the logging tool through the zone of interest. In this posture, a momentary interruption is encountered while the mud flow is used to force the wet connector and associated logging cable through the drill string until it lands at the logging tool. Connection is made and the logging procedure is then started. When the wet connector is pumped down, there is no need to reposition the logging tool because the position is already assured relative to the zone of interest. Ordinarily, logging proceeds by retrieving the logging tool from the borehole. Assume as an example that the zone of interest encompasses 500 feet of the deviated well. The logging tool is initially pushed to the top of the 500 foot zone, the wet connector is pumped down, connection is made, and then 500 feet of drill pipe is added and pushed beyond the the 500 ffoot zone. Then 500 foot of drill pipe is removed at the surface during logging on tool retrieval. The drill pipe is first simply pushed into and then pulled from the deviated well. This pushes the properly oriented logging tool to the end of the 500 foot zone. Then, the 500 foot of drill pipe is removed one joint at a time as the logging tool is pulled back through the 500 foot zone of interest. Logging occurs at the necessary locations appropriate for the investigation. At all points in time, the logging time is properly oriented relative to the gravity vector in the zone of interest so that it is positioned for obtaining data with proper orientation. As noted above, this orientation also includes proper contact relative to the walls of the open borehole which controls tool standoff to the formation.
At the time of connection between the wet connectors, pump down forces the logging cable connected to a weight bar and a female wet connector through the drill string. This exposes the mating connectors to very high ambient pressures, 10,000 psi or higher. The drill string is filled with drilling mud which seriously interferes with proper operation of the wet connectors. The wet connectors are shielded so that they are not exposed to the drillng mud at the contact area. So to speak, the contacts are wiped clean before mating contact is made. This mating system in conjunction with a latching system accomplishes connection at a controlled rate. This overcomes excessive velocity of the female wet connector should it bang or jolt the male wet connector. Thus, latching is achieved controllably with a locking stroke whereby the cooperative connectors are wiped before connection, telescoped together, brought into operative electrical connection, latched, all in a secure location without regard to the external environment.
The present disclosure is thus summarized as a drill pipe conveyed logging (DPCL) system which supports a logging tool in a protective housing equipped with rotary standoffs to control standoff spacing. The housing is aligned with the drill pipe and encloses the logging tool on the interior. The housing protects the entire tool except that certain portions are cut away. This permits backup shoes to extend from the housing. The backup arm (caliper) is used to measure the diameter of the borehole. Normally, it does decentralize the logging tool. However, decentralization is achieved by other means. Moreover, the logging tool is forced to the low side of the deviated well by incorporation of a low side weight system therein. This in conjunction with the rotary standoffs assures proper orientation. The upper end of the protective housing encloses a male wet connector in conjunction with a serial centralizer thereabove to guide and direct the female wet connector into contact. The wet connectors achieve the desired connection with shielded contacts making the actual electrical connection. The apparatus and a method of use will be set forth in greater detail hereinafter on reference to the drawings in conjunction with the written specification found below.